This application claims priority to Japanese patent application Nos. JPAP11-218878 filed on Aug. 2, 1999 and JPAP 11-218885 filed on Aug. 2, 1999 in the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention:
The present invention relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming that is capable of effectively generating a consistent charge potential.
2. Description of the Background:
Charging the surface of a photoconductive member is one of basic and important processes performed in an image forming apparatus using an electrophotographic method, such as a copying machine, a facsimile machine, a printer, and so forth. There have been developed various techniques for consistently charging the surface of the photoconductive member, which are classified in two types. In a first type, which is referred to as a contact type charging technique, a charging member is configured to make its surface contact the photoconductive member so as to provide charges evenly to the surface of the photoconductive member. In a second type, which is referred to as a non-contact type charging technique, a charging member is configured to be closely adjacent to the photoconductive member so as to provide a small gap between the charging member and the photoconductive member.
The non-contact type charging has an advantage in the performance of a charging operation, particularly in evenly charging the surface of the photoconductive member. However, the non-contact type charging has a drawback of a production of ozone. Therefore, the contact type is now becoming a mainstream.
However, the contact type charging also has several drawbacks due to its mechanism which causes the charging member such as a charging roller to directly contact the surface of the photoconductive member. For example, the photoconductive member will be contaminated due to the contact with the charging roller so that an abnormal image will be produced. The photoconductive member may develop a crack at a place on the surface contacting the charging roller if an excess contact pressure is applied onto the surface of the photoconductive member.
Further, the charging roller itself may be contaminated by the toner deposited on the photoconductive member. If the limit of the contamination is violated, the charging roller reduces the charge performance, particularly the consistency of the charge.
Further, the surface of the photoconductive member may be worn by the contact of the charging roller and the charge potential is reduced.
In addition, if the photoconductive member has a pinhole, it has not a sufficient margin against a leakage of the charge through the pinhole.
In order to avoid these problems, the charging roller is arranged to merely have an extreme small gap relative to the photoconductive member and to charge the photoconductive member from that distance. However, if the charging roller is made of an elastic material, it is difficult to make such a gap in an accurate cost-effective manner.
Accordingly, the present invention provides a novel charging apparatus in view of the above discussion.
In one example, a novel charging apparatus includes a charging member which is arranged to be adjacent to a photoconductive member with a gap having a tolerance in a charging region relative to the photoconductive member and is applied with a voltage including a direct current voltage under a constant voltage control including an alternating current element to apply a charge to the photoconductive member. The above-mentioned alternating current element has a peak-to-peak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance.
The charging member may be a rotatable elastic roller.
The photoconductive member may be a rotatable photoconductive drum or belt.
The tolerance of the gap may be caused by an inaccurate flatness of a surface of the charging member.
The tolerance of the gap may be caused by inaccuracy of parallel alignment of the charging member and the photoconductive member.
The maximum gap may be greater than a maximum gap requiring a charge-start voltage greater than the charge-start voltage required in a case when the gap is substantially 0.
The charging member may be arranged to be adjacent to and partly contact the photoconductive member so as to partly form the gap having the tolerance.
The present invention further provides a novel charging method. In one example, the novel charging method includes the steps of providing, superposing, and applying. The providing step provides a charging member to form a gap having a tolerance in a charging region relative to a photoconductive member. The superposing step superposes an alternating current element to a direct current voltage under a constant voltage control. In this case, the alternating current element has a peak-to-peak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance. The applying step applies the direct current voltage with the superposed alternating current element to the charging member to apply a charge to the photoconductive member.
Further, the present invention provides an image forming apparatus. In one example, a novel image forming apparatus includes a photoconductive member and a charging apparatus. The charging apparatus charges the photoconductive member and includes a charging member arranged to be adjacent to the photoconductive member to form a gap having a tolerance in a charging region relative to the photoconductive member. The charging member is applied with a direct current voltage under a constant voltage control including an alternating current element to apply a charge to the photoconductive member. In this case, the alternating current element has a peak-to-peak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance.
Further, the present invention provides a charging apparatus. In one example, a novel charging apparatus includes a charging member which is arranged to be adjacent to a photoconductive member with a gap having a tolerance in a charging region relative to the photoconductive member and is applied with a voltage including a direct current voltage under a constant voltage control including an alternating current element under a constant current control to apply a charge to the photoconductive member. In this case, the alternating current element has a peak-to-peak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance.
The charging member may be a rotatable elastic roller.
The photoconductive member may be a rotatable photoconductive drum or belt.
The tolerance of the gap may be caused by an inaccurate flatness of a surface of the charging member.
The tolerance of the gap may be caused by inaccuracy of parallel alignment alignment of the charging member and the photoconductive member.
The maximum gap may be greater than a maximum gap requiring a charge-start voltage greater than the charge-start voltage required in a case when the gap is substantially 0.
The charging member may be arranged to be adjacent to and partly contact the photoconductive member so as to partly form the gap having the tolerance.
Further, the present invention provides a charging method. In one example, a novel charging method includes the steps of providing, superposing, and applying. The providing step provides a charging member to form a gap having a tolerance in a charging region relative to a photoconductive member. The superposing step superposes an alternating current element under a constant current control to a direct current voltage under a constant voltage control. In this case, the alternating current element has a peak-to-peak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance. The applying step applies the direct current voltage with the superposed alternating current element to the charging member to apply a charge to the photoconductive member.
Further, the present invention provides a novel image forming apparatus. In one example, a novel image forming apparatus includes a photoconductive member and a charging apparatus. The charging apparatus charges the photoconductive member and includes a charging member arranged to be adjacent to the photoconductive member to form a gap having a tolerance in a charging region relative to the photoconductive member. The charging member is applied with a direct current voltage under a constant voltage control including an alternating current element under a constant current control to apply a charge to the photoconductive member. In this case, the alternating current element has a peak-topeak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance.
Further, the present invention provides a charging apparatus. In one example, a novel charging apparatus includes a charging member which is arranged to be adjacent to a photoconductive member to form a gap having a tolerance in a charging region relative to the photoconductive member and is applied with a direct current voltage under a constant voltage control including an alternating current element to apply a charge to the photoconductive member. In this case, the gap has a mean value at each position in the charging region in longitudinal and circumference directions of the charging member is greater than 10 xcexcm and of which deviation is greater than 10 xcexcm relative to the mean value. Further, the alternating current element has a peak-to-peak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance.
The charging member may be a rotatable elastic roller.
The photoconductive member may be a rotatable photoconductive drum or belt.
The gap may be formed with an intermediate member to be placed between the charging member and the photoconductive member and a thickness of the intermediate member determines the maximum gap.
The charging member may be arranged to be adjacent to and partly contact the photoconductive member so as to partly form the gap having the tolerance.
Further, the present invention provides a novel charging method. In one example, a novel charging method includes the step of providing and applying. The providing step provides a charging member to form a gap having a tolerance in a charging region relative to the photoconductive member. In this case, the gap has a mean value at each position in the charging region in longitudinal and circumference directions of the charging member is greater than 10 xcexcm and a deviation of the predetermined gap relative to the mean value is greater than 10 xcexcm. The applying step applies to the charging member a direct current voltage under a constant voltage control including an alternating current element to charge the photoconductive member. In this case, the alternating current element has a peak-to-peak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance.
Further, the present invention provides a novel image forming apparatus. In one example, a novel image forming apparatus includes a photoconductive member and a charging apparatus for charging the photoconductive member. The charging apparatus includes a charging member which is arranged to be adjacent to the photoconductive member to form a gap having a tolerance in a charging region relative to the photoconductive member and is applied with a direct current voltage under a constant voltage control and an alternating current element to apply a charge to the photoconductive member. In this case, the gap has a mean value at each position in the charging region in longitudinal and circumference directions of the charging member is greater than 10 xcexcm and of which deviation is greater than 10 xcexcm relative to the mean value. Further, the alternating current element has a peak-to-peak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance.
Further, the present invention provides a charging apparatus. In one example, a novel charging apparatus includes a charging member which is arranged to be adjacent to a photoconductive member to form a gap having a tolerance in a charging region relative to the photoconductive member and is applied with a direct current voltage under a constant voltage control including an alternating current element under a constant current control to apply a charge to the photoconductive member. In this case, the gap has a mean value at each position in the charging region in longitudinal and circumference directions of the charging member is greater than 10 xcexcm and of which deviation is greater than 10 xcexcm relative to the mean value.
The charging member may be a rotatable elastic roller.
The photoconductive member may be a rotatable photoconductive drum or belt.
The charging member may have a volume resistance ratio of 105 xcexa9m or more.
The charging member may be arranged to be adjacent to and partly contact the photoconductive member so as to partly form the gap having the tolerance.
Further, the present invention provides a novel charging method. In one example, a novel charging method includes the steps of providing and applying. The providing step provides a charging member to form a gap having a tolerance in a charging region relative to the photoconductive member. In this case, the gap has a mean value at each position in the charging region in longitudinal and circumference directions of the charging member is greater than 10 xcexcm and a deviation of the predetermined gap relative to the mean value is greater than 10 xcexcm. The applying step applies to the charging member a direct current voltage under a constant voltage control including an alternating current element under a constant current control to apply a charge to the photoconductive member. In this case, the alternating current element has a peak-to-peak voltage at least twice as great as a charge-start voltage to be applied to the charging member at a maximum gap within a range of the gap having the tolerance.
Further, the present invention provides a novel image forming apparatus. In one example, a novel image forming apparatus includes a photoconductive member and a charging apparatus. The charging apparatus charges the photoconductive member and includes a charging member which is arranged to be adjacent to the photoconductive member to form a gap having a tolerance in a charging region relative to the photoconductive member and is applied with a direct current voltage under a constant voltage control and an alternating current element under a constant current control to apply a charge to the photoconductive member. In this case, the gap has a mean value at each position in the charging region in longitudinal and circumference directions of the charging member is greater than 10 xcexcm and of which deviation is greater than 10 xcexcm relative to the mean value.